Composition Process And Apparatus To Remove Sulfur From Refined Crude Oil Fraction

ABSTRACT

A ionic liquid composition to remove sulfur from refined crude oil fraction, comprising or consisting of two or more compounds having: —an imidazolium cation substituted by one or more straight or branched C 1 -C 6  alkyl group and —an anion selected from the group consisting of R 5 COO, CI., Br, [BF 4 ], [PF 6 ]—, [SbF 6 ]—, [R 6 SO 4 ], [OTs], [OMs], wherein R5 is C 1 -C 8  alkyl, Cs—Cs cycloalkyl, benzyl, C 2 -C 6  alkenyl, and R6 is C 1 -C 6  alkyl.

FIELD OF THE INVENTION

The present invention relates to a composition, a process and anapparatus to remove sulfur from refined crude oil fraction, inparticular from heavy fuel oils, more in particular from fuel oils usedin marine transportation.

BACKGROUND OF THE INVENTION

Crude oil is a complex mixture of hydrocarbon compounds, generallyviscous, dark greenish-brown fluids due to the variety of compoundspresent in them. The physical properties including viscosity, volatilityand density, vary considerably depending upon the source. The proportionof elements in crude oil generally varies in the following ranges:carbon (83-87%), hydrogen (10-14%), sulfur (0.02-8%), nitrogen (0.1-2%),oxygen (0.05-1.5%) with small quantities of metallic constituents suchas vanadium and nickel which are less than 1000 ppm. Sulfur, oxygen,nitrogen and metals make up most impurities found in crude oil. Thesulfur content of crude oil is an important characteristic which effectsthe oil price.

Crude oil can be separated into different boiling point fractions,common refined fractions of crude oil include gasoline, kerosene, dieseloil, heavy oil, and lubricating oil. The refined fractions derived fromcrude oil have physical and chemical characteristics that differaccording to the type of crude oil and the subsequent refiningprocesses. Generally, as the fraction becomes heavier a) theconcentration of sulfur containing species increases; b) more of thesulfur is contained in thiophenic structures; c) there is an increase infouling species, such as metals and coke precursors; d) the density,molecular mass, boiling point temperature, and viscosity increase; e)increasing asphalthene content and precipitation tendency are observed.

The refined crude oil fractions are commonly used as energy resource andas fuel in the transportation sector, the last one representing around20% of the global energy consumption and is the biggest consumer of oilin the world. Sulfur contained in the refined crude oil fraction isconverted by combustion to SOx, which is a major source of acid rain,thus the presence of sulfur species is clearly a major issue in airpollution, airborne particulate emission and public health.

Specifications that govern fuels, in particular transportation fuels,have over the years become increasingly stringent with respect to sulfurcontent. For environmental protection purpose, many countries havemandated reduction of sulfur level in diesel and gasoline fuel down to10 ppm. Moreover, the International Maritime Organization (IMO)announced the implementation of a global sulfur limit of 0.5% m/m(mass/mass) in ship fuel by 2020. Therefore, to continue using refinedfractions of crude oil it is urgent to set up efficient and affordabledesulfurization procedures.

Many fuel desulfurization methods are known, such as catalytichydrodesulfurization (HDS), extractive desulfurization, either withtraditional solvents and ionic liquids, oxidative desulfurization,biodesulfurization and desulfurization through alkylation,chlorinolysis, and by using supercritical water. None of the methodsreported above are able to eliminate completely S-compounds from fuels.

Commercially, catalytic methods such as hydrodesulfurization (HDS) andsome chemical processes for sulfur compounds reductions are the mostcommonly applied techniques. In the HDS technology the fuel is heatedand mixed with H₂ gas before being fed into a fixed bed reactor thatcontains pelleted catalyst known as the “hydrotreater”. The operationaltemperature of the hydrotreater is commonly in the range of 300-380° C.and the pressure is above 30 bar, thus this method requires high energyand consumes large amount of hydrogen.

Alternative methods to classical HDS processes include extraction,oxidation, precipitation, adsorption, distillation and alkylation.Extractive desulfurization (EDS) depends upon the different partitioningof sulfur compounds between the organic phase and the extractant phase.EDS does have some advantages in that it is simple and can be carriedout at moderate conditions in term of pressure and temperature, withoutusing a catalyst or hydrogen gas. The selectivity of an extractivesolvent is an important factor in EDS design as it controls efficiency,reusability and recyclability. In petroleum and hydrocarbon industry,various solvents such as ethers, amines in alcohols and other volatileorganic compounds have been used. Conventional solvents have limitationsin terms of environmental issue and recycle ability, as a difficultywith the technique is regenerating the extractive solvent.

Ionic liquids (IL), also called liquid electrolytes, ionic mets, ionicfluids, fused salts, liquid salts or ionic glasses are a new class ofoutstanding good solvents miscible with water or organic solvents, theycan be liquid at temperatures of −96° C. and some are liquid at over400° C. Ionic liquids' low volatility makes them desirable substitutesfor volatile organic compounds (VOCs). ILs consist of organic cations,such as ammonium, choline, imidazolium, phosphonium, pyrazolium,pyridinium, pyrrolidinium, quinolinium and sulfonium, and a wide rangeof anions such as halides, tetrafluoroborate, hexafluorophosphate,bistriflimide, triflate and tosylate.

Recently, researchers have used ILs for extractive desulfurisation (EDS)in place of molecular solvents. For example, the use ofimidazolium-based ion liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM]PF₆ or 1-butyl-3-methylimidazolium tetrafluoroborate[BMIM]BF₄ as extractive agents for the removal of S-compounds from modelfuels as well as real fuels such as diesel and gasoline has beendescribed in Dharaskar, S. A. et al in 3dr International Conference onChemical, Agricultural and Medical Sciences (CAMS-2015) December 10-11Singapore (http://dx.doi.org/10.15242/IICBE.C1215007). The diesel/ILmass ratio as well as the gasoline/IL mass ratio reported therein is5:1; the S-removal % is comprised between 41.5% and 61.1%.

The use of 1-ethyl-3-methylimidazolium diethylphosphate [EMIM]DEP] inthe desulfurization of diesel oil has been described by Seeberg, A. J.et al., in Green Chem (2010) 12: 602-608; the authors have found thatthe efficiency of the extraction increases if the S-species arepreviously oxidized to the corresponding sulfoxides and sulfones. Thediesel/IL mass ratio reported therein is 1:1.

Heavy Fuel Oil (HFO) is characterized by a high content of sulfurcompounds and by the refractory nature of the sulfur compounds presentin the oil. Moreover, HFO has high viscosity and high boiling point.Since heavy fuel oils generate high calorie and are relativelyinexpensive, a large amount of heavy fuel oil is consumed all over theworld for facilities in various industries including stationarycombustion for the production of steam for industrial uses or forgenerating electricity. Heavy fuel oil is also used in marinetransportation.

As reviewed by Javadi, R et al. in Appl Petrochem Res (2012), 1:3-19,few of the known technologies are viable and/or efficient for thedesulfurization of heavy oil, mainly due to the properties of heavy oilitself. Javadli et al. reports that although ionic liquids have a highdistribution coefficient for sulfur compounds such as dibenzothiophenein model mixtures, the distribution coefficient in real straight rundistillate is rather low, and even worse in heavy fuel oils; therefore,ionic liquid are not ideal solvents for extractive desulfurization ofreal straight run distillates, in heavy oil the situation becomes worse.Moreover, as ionic liquids are high boiling solvent, the recovery ofextracted sulfur compounds is more challenging than with organicsolvents. For example, direct removal of sulfur compounds from ionicliquids by distillation is not applicable to heavy oil as the boilingpoint of heavier organosulfur compounds present in the heavy oil, suchas alkylated dibenzothiophenes, are high (>340° C.) and it would requirevacuum distillation. Re-extraction of sulfur compounds withlow-boiling-point solvent would require an additional separation step.Addition of water to ionic liquids to reduce the distributioncoefficient of sulfur compounds in ionic liquids requires the finalremoval the water, a step which requires energy consumption.

According to Javadli et al. there are no reports on the extractivedesulfurization of heavy oil by ionic liquids. Javadli et al. teachesthat the approach with the best chance of leading to a breakthrough indesulfurization of heavy oil is autoxidation followed by thermaldecomposition of the oxidized heavy oil; there is also scope forsynergistically employing autoxidation in combination withbiodesulfurization and hydrodesulfurization.

The effective desulfurisation of the refined crude oil fractions needto 1) reduce the amount of pollutants in air, 2) employ the minimumenergy during the desulfurisation process), 3) have a minimal effect onthe price of the fuel.

In view of the above, there is still the need to find improved methodsfor desulfurization of refined crude oil fractions, in particular fordesulfurization of heavy fuel oil, more in particular from fuel oilsused in marine transportation.

SUMMARY

The Applicant has faced the problem of improving the desulfurization ofrefined crude oil fractions and has found a composition comprisingspecific ionic liquids which is useful for extractive desulfurization ofsuch oil fractions; surprisingly this composition is useful also for theextractive desulfurization of oils having an high sulfur content such asheavy fuel oil, in particular marine fuel oil.

As will be discussed deeply in the experimental part, the Applicant hasfound that the ionic liquids composition according to the invention isable to effectively remove sulfur from marine fuel oil by extraction. Inparticular, the Applicant has found that desulfurization of marine fueloil by extraction with the ionic liquids composition according to theinvention in combination with specific process conditions is able toremove more than 90% of the sulfur from marine fuel oil without theaddition of any oxidizing agent. For example, without the addition of aperoxide, such as hydrogen peroxide, sodium peroxide or an organicperoxide. Without being linked to any theory, the Applicant speculatesthat the specific ionic liquid composition of the invention at thespecific process conditions exercises itself an oxidizing action.

Moreover, the ionic liquid composition of the invention is capable ofbeing reused multiple times, until a maximum of 5 times.

It is thus an object of the present invention to provide a ionic liquidcomposition designed to improve desulfurization of refined crude oilfractions with respect to the prior art.

It is also object of the present invention to provide a process and anapparatus for desulfurization which allow to improve desulfurization ofrefined crude oil fractions with respect to the prior art.

It is in particular object to improve desulfurization of heavy fuel oilfor marine transportation.

In particular, it is object of the present invention to increase theamount of sulfur removed by extraction with the ionic liquidcomposition.

Another object of the present invention is to shorten the extractiontime.

It is also object of the present invention to reduce costs related todesulfurization of refined crude oil fractions.

These and other objects are achieved through a ionic liquid composition,a process and an apparatus designed to lower the concentration of bothheavy metals and sulfur within crude oil fractions, in particular heavyfuel oil, in particular marine fuel products. The working principle isbased on emulsification with ionic liquids containing specific taskacids. Once a selected quantity of fuel and ionic liquids are blendedand satisfactory emulsified, it is passed through a catalytic reactor.The catalytic reactor/process is arranged inline between a mixing tankand a settling tank. The catalytic process binds heavy metals includingall sulfur to the ionic liquids. Due to difference in gravity, theemulsion is left to settle in a separate tank. When settled, theprocessed oil is transferred to a service tank or separate clean storagetank for use when needed. The settled ionic liquids containing heavymetals and sulfur is transferred to a separate flashing unit. Theflashing separates the ionic liquids from the heavy metals and sulfur,which is left as a sludge residue within the flashing unit. The ionicliquids are capable of being reused multiple times. The sludge residueis transferred to holding tanks or to separate drying and bagging unitfor further handling.

In a first aspect, the present invention relates to a ionic liquidcomposition comprising or consisting of two or more compounds having

-   -   an imidazolium cation substituted by one or more straight or        branched C₁-C₆ alkyl group and    -   an anion selected from the group consisting of R₅COO⁻, Cl⁻, Br⁻,        [BF₄]⁻, [PF₆]⁻, [SbF₆]⁻, [R₆SO₄]⁻, [OTs]⁻, [OMs]⁻, wherein R5 is        C₁-C₆ alkyl, C₃-C₈ cycloalkyl, benzyl, C₂-C₆ alkenyl, and R6 is        C₁-C₆ alkyl.

In an aspect according to the first aspect, the imidazolium cation issubstituted in position 1 and 3 by a straight or branched C₁-C₆ alkylgroup, more preferably is substituted in position 1 by butyl and inposition 3 by methyl.

In an aspect according to the first aspect, the anion is selected fromCl⁻, [BF₄]⁻ and [PF₆].

In an aspect according to the first aspect, a suitable ionic liquid is1-butyl-3-methyl imidazolium hexafluoro phosphate.

In an aspect according to the first aspect, another suitable ionicliquid is 1-butyl-3-methyl imidazolium tetrafluoroborate.

In an aspect according to the first aspect, a further suitable ionicliquid is 1-butyl-3-methyl imidazolium chloride.

In an aspect according to the first aspect, the composition comprises orconsists of

-   -   1-butyl-3-methyl imidazolium hexafluoro phosphate,    -   1-butyl-3-methyl imidazolium tetrafluoroborate, and    -   1-butyl-3-methyl imidazolium chloride.

In an aspect according to the first aspect, the composition comprises orconsists of:

-   -   from 30 to 50% by volume, such as from 35 to 44% by volume or        from 40 to 45% by volume of 1-butyl-3-methyl imidazolium        hexafluoro phosphate,    -   from 20 to 30% by volume, such as from 22 to 27% by volume or        from 26 to 29% by volume of 1-butyl-3-methyl imidazolium        tetrafluoroborate,    -   from 25 to 35% by volume, such as from 26 to 29% by volume or        from 28 to 32% by volume of 1-butyl-3-methyl imidazolium        chloride        with respect to the total volume of the composition.

In an aspect according to the previous aspects, the volume ratio between1-butyl-3-methyl imidazolium hexafluoro phosphate, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methyl imidazolium chlorideis comprised between 1:0.63:0.74 and 1:0.61:0.66.

The composition does not require an oxidizing agent.

The composition does not require a metal salt, e.g. a salt of a GroupIB, IIB, VIB, or VIIIB metal, such as a salt of copper, nickel, zinc,cobalt, molybdenum, silver or palladium.

The composition may additionally comprise water (e.g. demineralizedwater) and/or an organic solvent (e.g. methanol). The organic solventmay be polar. Suitable organic solvents include methanol, ethanol,propanol, butanol, acetone, butan-2-one, tetrahydrofuran, methylacetate, ethyl acetate, and/or acetonitrile).

The two or more compounds may constitute at least 0.5%, at least 1% atleast 3%, at least 5%, at least 10%, at least 20%, at least 30%, atleast 50%, at least 70%, at least 80%, at least 90% at least 95%, atleast 97%, at least 98% or at least 99% of the composition and/or thetwo or more compounds may constitute 99% or less, 98% or less, 95% orless, 90% or less, 70% or less, 50% or less, 25% or less, 10% or less,5% or less, 3% or less or 2% or less of the composition. Percentages maybe by mass or volume.

In a second aspect, the present invention relates to the use of theionic liquid composition, according to one or more of the previousaspects, as extractive agents for the removal of S-compounds from arefined crude oil fraction.

In an aspect according to the second aspect, suitable refined crude oilfractions are selected from gasoline, kerosene, diesel oil, heavy oil,and lubricating oil, optionally is heavy oil.

In an aspect according to the second aspect, the refined crude oilfraction is heavy fuel oil for maritime transportation.

In an aspect according to the second aspect, the S-removal % is higherthan 70%, optionally is higher than 75%, 80% or 85%, optionally ishigher than 90%.

In a third aspect, the present invention relates to an emulsioncomprising:

-   -   a mixture comprising the ionic liquid composition according to        one or more of the previous aspects of the invention and        demineralized water, and    -   a refined crude oil fraction.

The invention also resides in the mixture, i.e. a composition comprisingor consisting of water; and

two or more compounds having:

-   -   an imidazolium cation substituted by one or more straight or        branched C₁-C₆ alkyl group;    -   an anion selected from the group consisting of R₅COO⁻, Cl⁻, Br⁻,        [BF₄]⁻, [PF₆]⁻, [SbF₆]⁻, [R₆SO₄]⁻, [OTs]⁻, [OMs]⁻, wherein R5 is        C₁-C₆ alkyl, C₃-C₈ cycloalkyl, benzyl, C₂-C₆ alkenyl, and R6 is        C₁-C₆ alkyl.

The two or more compounds may constitute from 1% to 3% by mass of thecomposition and the water may constitute from 97% to 99% by mass ofcomposition, with respect to the total mass of the composition.

In a fourth aspect, the present invention relates to a process fordesulfurization of a crude oil fraction through the ionic liquidcomposition of one or more of the previous aspects.

In an aspect according to the fourth aspect, the process comprises:

-   -   mixing a ionic liquid composition according to any of the        previous aspects with a batch of refined crude oil fraction in a        mixing tank to manufacture an emulsion comprising at least the        refined crude oil fraction and the ionic liquid composition;    -   feeding the emulsion through a catalytic reactor to bind at        least S-compounds, and optionally other metals, of the refined        crude oil fraction to the ionic liquid composition;    -   feeding the emulsion into a settling tank and storing the        emulsion in said settling tank for a settling time in order to        leave the S-compounds bond to the ionic liquid composition to        separate by gravity from a desulfurized refined crude oil        fraction and to settle down in the settling tank.

In an aspect according to the fourth aspect, the desulfurized refinedcrude oil fraction is then transferred to a storage or service tank.

In an aspect according to the fourth aspect, the settled ionic liquidcomposition containing S-compounds is then transferred to a flashingunit.

In an aspect according to the fourth aspect, before mixing the ionicliquid composition with the batch of refined crude oil fraction, theionic liquid composition is mixed with demineralized water and then themixture of ionic liquid composition and demineralized water is fed tothe mixing tank containing or configured to contain the batch of refinedcrude oil fraction.

In an aspect according to the fourth aspect, in the flashing unit,S-compounds are separated from the ionic liquid composition and form aresidual sludge in said flashing unit.

In an aspect according to the previous aspect, the ionic liquidcomposition free of S-compounds is fed to a separate re-use tank to bereused in the process and/or the residual sludge is transferred toholding tank and, optionally, dried and packed for further handling.

In an aspect according to the fourth aspect, the emulsion in the mixingtank is maintained at a mixing temperature between 60° C. and 100° C.,optionally of 80° C.

In an aspect according to the fourth aspect, the emulsion in thesettling tank is maintained at a settling temperature between 40° C. and60° C., optionally of 50° C.

In an aspect according to the fourth aspect, the settling time isbetween 60 min and 180 min, optionally of 120 min.

In an aspect according to the third or the fourth aspect, the emulsioncomprises:

-   -   from 5% to 20% by mass of a mixture comprising the ionic liquid        composition according to the first object of the invention and        demineralized water, and    -   from 80% to 95% by mass of a refined crude oil fraction, with        respect to the total mass of the emulsion.

More preferably, according to the third object of the invention, theemulsion comprises:

-   -   from 5% to 15% by mass of a mixture comprising the ionic liquid        composition according to the first object of the invention and        demineralized water, and    -   from 85% to 95% by mass of a refined crude oil fraction,

with respect to the total mass of the emulsion,

In an aspect according to the third or the fourth aspect, the abovemixture comprises from 1% to 3% by mass of the ionic liquid compositionand from 97% to 99% by mass of demineralized water, with respect to thetotal mass of the mixture.

In an aspect according to the third or the fourth aspect, the water isdemineralized through a reverse osmosis system.

In an aspect according to the third or the fourth aspect, a mass ratiobetween the oil fraction and the ionic liquid composition is 550:1, morepreferably is 450:1.

In an aspect according to the third or the fourth aspect, suitablerefined crude oil fractions are selected from gasoline, kerosene, dieseloil, heavy oil, and lubricating oil, preferably is heavy oil.

In an aspect according to the third or the fourth aspect, the refinedcrude oil fraction is heavy fuel oil for maritime transportation.

In a fifth aspect, the present invention relates to an apparatus fordesulfurization of a refined crude oil fraction configured to performthe process of the fourth aspect.

In an aspect according to the fifth aspect, the apparatus comprises:

a mixing tank having a first inlet in fluid communication with a tank ofrefined crude oil fraction;

a fresh ionic liquid composition tank and/or a re-use ionic liquidcomposition tank in fluid communication with a second inlet of themixing tank;

at least one settling tank having an inlet in fluid communication withan outlet of the mixing tank;

wherein said at least one settling tank has a first upper outlet fordelivering desulfurized refined crude oil fraction and a second loweroutlet for delivering settled ionic liquid composition containingS-compounds;

-   -   a catalytic reactor located between the outlet of the mixing        tank and the inlet of said at least one settling tank.

In an aspect according to the previous aspect, the apparatus comprises aflashing unit configured to separate the S-compounds from the ionicliquid composition; wherein the flashing unit has an inlet connected tothe second lower outlet of said at least one settling tank for receivingthe settled ionic liquid composition containing S-compounds, a firstupper outlet in fluid communication with an inlet of the re-use tank fordelivering the ionic liquid composition free of S-compounds to saidre-use tank, a second lower outlet for delivering residual sludgeS-compounds.

In an aspect according to the fifth aspect, the catalytic reactorcomprises mixing devices configured to further mix emulsion flowingthrough the catalytic reactor and to increase the rate of chemicalreactions in the emulsion.

Definitions

HFOs are classified according to different parameters by differentorganizations so there are different numerical specifications for heavyfuel oil grades.

ASTM D396 classifies heavy fuel oils as oils number 4 to 6 on the baseof their viscosity. In general, the boiling point and carbon chainlength of the fuel increases with fuel oil number; the higher themolecular weight of the oil's component, the higher the level ofpolyaromatic compounds, polycycloparaffins and hetero-atoms (N, O, S andmetals) increase, and the lower the level of paraffins; viscosity alsoincreases with number and the heaviest oil has to be heated to get it toflow. Price usually decreases as the fuel number increases.

In the UK, the British Standard BS 2869 assigns Class G or H to heavyfuel oil on the base of their viscosity and sulfur content.

In the European Union the Engler degree is generally used to classifyfuels: heavy fuel oils are oils having a viscosity greater than 12°Engler at 50° C.

In Russia, Mazut is the term denoting residual fuel oil, “furnace mazut”is the heaviest residual fraction of the crude, almost exactlycorresponding to US Number 6 fuel oil and further graded by viscosityand sulfur content.

In the maritime field, another type of classification is used for fueloils; according to that classification, marine fuel oil is a synonym ofheavy fuel oil and denotes a pure or nearly pure residual oil, roughlyequivalent to US Number 6 fuel oil.

As used herein, with the expressions “heavy fuel oil”, “heavy oil”,“heavy fuel”, “residual fuel oil”, “residual oil”, “residual fuel”,“marine fuel oil”, “marine oil” and “marine fuel” we mean the productsthat consist primarily of the residuum of the refiring process aftervirtually all of the higher quality hydrocarbons have been removed fromcrude oil feedstock. With the above expressions as used herein, bothpure heavy oil and mixtures containing mainly heavy oil are meant. Amongthe heavy fuel oils that can be utilized more effectively because of theinvention are oils classified as number 4 to 6 according with ASTM D396as well as those having a viscosity value higher than 12° Engler at 50°C.

DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows an apparatus for desulfurization of a refinedcrude oil fraction according to the present invention; and

FIG. 2 is a flowchart of a process for desulfurization of a refinedcrude oil fraction according to the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically shows an apparatus 1 for desulfurization of arefined crude oil fraction according to the present invention.

Suitable refined crude oil fractions may be selected from gasoline,kerosene, diesel oil, heavy oil, and lubricating oil. In an embodiment,the refined crude oil fraction is heavy fuel oil for maritimetransportation.

The apparatus 1 comprises a mixing tank 2 having a first inlet 2 a influid communication with a tank 3 of refined crude oil fraction and asecond inlet 2 b in fluid communication with a fresh ionic liquidcomposition tank 4 and/or a re-use ionic liquid composition tank 4′. Themixing tank 2 comprises mixing elements, not shown in drawings,configured to blend the liquid content of the mixing tank 2. The mixingtank 2, including flanges and connections, may be assembled of weldedmild steel plates, rockwool insulation and galvanized cover plates. Themixing elements of the mixing tank 2 of the disclosed embodimentcomprise two macerating pumps, one duty and one stand-by, to ensuresatisfactory emulsification. The macerating pumps operates in on/offmode for each batch. Continuously level control, including temperaturemonitoring, may be displayed locally as well as on a remote controlsystem. The mixing tank 2 is equipped with heating devices 5, such asinternal steam heating coils and/or electrical heating elements withtemperature control.

According to the process of the invention, batches of refined crude oilfraction from the tank 3 are processed. For each batch, a predeterminequantity of refined crude oil fraction is transferred to the mixing tank2. An amount of a mixture comprising a ionic liquid composition (whichwill be detailed in the present description) and demineralized watercalculated as a function of the actual sulfur content within the batchof refined crude oil fraction is transferred from the fresh ionic liquidcomposition tank 4 and/or from the re-use ionic liquid composition tank15 into the mixing tank 2. In the mixing tank, the refined crude oilfraction with the mixture comprising the ionic liquid composition andthe demineralized water is emulsified to obtain an emulsion comprising:the mixture comprising the ionic liquid composition and demineralizedwater, and the refined crude oil fraction. The refined crude oilfraction inlet supply should be maintained at approx. 60° C.-80° C. (apre-heater may be installed if necessary). The refined crude oilfraction with the mixture comprising the ionic liquid composition andthe demineralized water is heated to and maintained at a mixingtemperature T_(mix) of 80° C. through the heating devices 5 for a betteremulsification.

The apparatus 1 comprises two settling tanks 6, each having an inlet 6 ain fluid communication with an outlet 2 c of the mixing tank 2. Each ofthe settling tanks 6 has a first upper outlet 6 b connected to a storageor service tank 7 for refined crude desulfurized oil fraction resultingfrom the process of the invention and a second lower outlet 6 c. Thesettling tanks 6, including flanges and connections, may be assembled ofwelded mild steel plates, rockwool insulation and galvanized coverplates. Each settling tank 6 is equipped with internal cone baffleplates 8 to reduce the overall settling time. Each settling tank 6 isprovided with level and temperature controls which may be displayedlocally as well as on the remote control system. The emulsion is storedin said settling tanks 6 for a settling time t in order to leave thesulfur compounds (S-compounds) bond to the ionic liquid composition toseparate by gravity from a desulfurized refined crude oil fraction andto settle down in each settling tank 6. The emulsion in the settlingtanks 6 is maintained at a settling temperature T_(settl) of 50° C. forthe cited settling time “t” which may be of 120 minutes.

A catalytic reactor 9 is located between the outlet 2 c of the mixingtank and the inlets 6 a of the settling tanks 6. The catalytic reactor 9comprises duct or ducts, mechanical elements, e.g. blades, movable orfixed, or other mixing devices configured to further mix the emulsionflowing through the catalytic reactor 9 and to increase the rate ofchemical reactions in said emulsion. The catalytic reactor 9 allows toimprove binding of at least S-compounds, and optionally other metals, ofthe refined crude oil fraction to the ionic liquid composition. Thecatalytic process is arranged inline between the mixing tank 2 andsettling tanks 6.

After the settling time “t”, the liquid in each settling tank 6 isdivided in two parts: un upper part 10 of desulfurized refined crude oilfraction and a lower part 11 of the sulfur compounds (S-compounds) bondto the ionic liquid composition. A continuously double acting levelcontrol system allows monitoring the oil/liquid composition levelinterface.

The desulfurized refined crude oil fraction 10 is then transferred tothe storage or service tank 7 through the first upper outlets 6 b foruse when needed. The settled ionic liquid composition containingS-compounds 11 is then transferred to a flashing unit 12 part of theapparatus 1. The flashing unit 12 is configured to separate theS-compounds from the ionic liquid composition. The flashing unit 12leaves the heavy metals and sulfur as a sludge residue in the bottompart. The flashing unit 12 has an inlet 12 a connected to the secondlower outlet 6 c of each settling tank 6 for receiving the settled ionicliquid composition containing S-compounds 11. The flashing unit 12 has afirst upper outlet 12 b in fluid communication with an inlet 4′a of there-use tank 4′, for delivering the ionic liquid composition free ofS-compounds to said re-use tank 4′, and a second lower outlet 12 c fordelivering residual sludge S-compounds to a holding tank 13. Theresidual sludge S-compounds may be transferred to a separate drying andbagging unit, not shown, for further handling. The ionic liquidcomposition free of S-compounds fed to the separate re-use tank 4′ maybe reused in the process.

The fresh ionic liquid composition tank 4 has an outlet 4 a connected tothe second inlet 2 b of the mixing tank 2 through a duct. The re-useionic liquid composition tank 4′ has an outlet 4′b connected to saidduct between said outlet 4 a and said second inlet 2 b. The fresh ionicliquid composition tank 4 has a first inlet 4 b connected to a source ofdemineralized water 14 and a second inlet 4 c connected to an outlet 15a of a concentrate ionic liquid composition tank 15. The fresh ionicliquid composition tank 4 is also acting as a mixing tank betweenconcentrated ionic liquids supplied from the concentrate ionic liquidcomposition tank 15 and demineralized water supplied optionally througha reverse osmosis desalination system.

According to the process of the invention, before mixing the ionicliquid composition with the batch of refined crude oil fraction, theconcentrate ionic liquid composition from the concentrate ionic liquidcomposition tank 15 is mixed with demineralized water in the fresh ionicliquid composition tank 4 and then the mixture of ionic liquidcomposition and demineralized water is fed to the mixing tank 2containing or configured to contain the batch of refined crude oilfraction.

The apparatus 1 is designed for continuous safe monitored batchoperations. Operating pressures within mixing tank 2 and settling tanks6 are kept at atmospheric pressure and fuel oil temperature ismaintained below its flash point High temperatures are only presentwithin the tank steam heating coils 5, as well as, within the flashingtank 12. Partial vacuum may also be applied within the flashing tank 12.

The ionic liquid composition consists of two or more compounds having:

-   -   an imidazolium cation substituted by one or more straight or        branched C₁-C₆ alkyl group and    -   an anion selected from the group consisting of R₅COO⁻, Cl⁻, Br⁻,        [BF₄]⁻, [PF₆]⁻, [SbF₆]⁻, [R₆SO₄]⁻, [OTs]⁻, [OMs]⁻, wherein R5 is        C₁-C₆ alkyl, C₃-C₈ cycloalkyl, benzyl, C₂-C₆ alkenyl, and R6 is        C₁-C₆ alkyl.

In an embodiment, the composition comprises or consists of

-   -   1-butyl-3-methyl imidazolium hexafluoro phosphate,    -   1-butyl-3-methyl imidazolium tetrafluoroborate, and    -   1-butyl-3-methyl imidazolium chloride.

In an embodiment, the composition comprises or consists of

-   -   from 35 to 44% by volume of 1-butyl-3-methyl imidazolium        hexafluoro phosphate,    -   from 22 to 27% by volume of 1-butyl-3-methyl imidazolium        tetrafluoroborate,    -   from 26 to 29% by volume of 1-butyl-3-methyl imidazolium        chloride

with respect to the total volume of the composition.

In an embodiment, a volume ratio between 1-butyl-3-methyl imidazoliumhexafluoro phosphate, 1-butyl-3-methyl imidazolium tetrafluoroborate and1-butyl-3-methyl imidazolium chloride is comprised between 1:0.63:0.74and 1:0.61:0.66.

In an embodiment, the emulsion comprises:

-   -   from 5% to 20% by mass of a mixture comprising the ionic liquid        composition according to the first object of the invention and        demineralized water, and    -   from 80% to 95% by mass of a refined crude oil fraction

with respect to the total mass of the emulsion.

In an embodiment, the emulsion comprises:

-   -   from 5% to 15% by mass of a mixture comprising the ionic liquid        composition according to the first object of the invention and        demineralized water, and    -   from 85% to 95% by mass of a refined crude oil fraction

with respect to the total mass of the emulsion,

In an embodiment, the above mixture comprises from 1% to 3% by mass ofthe ionic liquid composition and from 97% to 99% by mass ofdemineralized water, with respect to the total mass of the mixture.

In an embodiment, a mass ratio between the oil fraction and the ionicliquid composition is 550:1, more preferably is 450:1.

The Applicant has found that the S-removal % obtained through theinvention may be higher than 70%, optionally higher than 75%, 80% or85%, optionally higher than 90%.

EXAMPLES Example 1: Preparation of the Ionic Liquid (IL1) Composition

A ionic liquid composition according to the present invention wasprepared with the following ingredients (all percentage by volume):

44% by volume of 1-butyl-3-methyl imidazolium hexafluoro phosphate,

27% by volume of 1-butyl-3-methyl imidazolium tetrafluoroborate,

29% by volume of 1-butyl-3-methyl imidazolium chloride.

To prepare 10 liters of a ionic liquid composition according to thepresent invention 4.4 liters of 1-butyl-3-methyl imidazolium hexafluorophosphate, 2.7 liters of 1-butyl-3-methyl imidazolium tetrafluoroborateand 2.9 liters of 1-butyl-3-methyl imidazolium chloride were mixed for 2hours at 25° C.

Example 2: Preparation of the Emulsion of Heavy Oil and IL

The ionic liquid composition prepared in example 1 was first mixed withdemineralized water, then the resultant mixture was added to the heavyoil in a mixing tank.

Specifically:

9.8 liters of demineralized water and define amount of the ionic liquidcomposition prepared in example 1 (2% by mass with respect to the totalmass of the mixture) were mixed;

90 liters of marine fuel oil (IFO) and define amount of the mixtureprepared above (10% by mass with respect to the total mass of theemulsion) were mixed in the mixing tank to give the title emulsion.

Example 3: Determination of Sulfur Content

The S-content was determined by X-Ray Fluorescence Spectrometer (XRF) bySGS Italia SPA, Genova, Italia according to the International StandardISO 8754, second edition 2003.

Initial sulfur content of the oil (Inlet oil) used to prepare theemulsion of example 2 and sulfur content of the oil recovered aftersubjecting the emulsion of example 2 to the process according to theinvention (Outlet oil) were determined.

Sulfur content and the S-removal % of each sample are reported in Table1.

TABLE 1 S-content S-content S-removal Sample (% m/m) (ppm) (%) Inlet oil2.23 22300 — Outlel oil 0.030 300 98.66

As can be seen from the results reported above, the IL1 compositionprepared in example 1 when emulsified with a marine fuel oil is able toeffectively remove sulfur from such oil.

As reported by Javadli, R et al. cited above, few of the knowntechnologies are viable and/or efficient for the desulfurization ofheavy oil, mainly due to the properties of heavy oil itself, and thereare no reports on the extractive desulfurization of heavy oil by ionicliquids.

Surprisingly, the Applicant has found that IL1 is able to deeply removesulfur (by more than 98%) from oils having high sulfur content, such asthe marine fuel oil used in example 2, whose initial sulfur content ishigher than 2% m/m (higher than 20000 ppm), moreover this accomplishmentis reached without the addition of any oxidizing agent.

Furthermore, it is worth noting that IL1 is able to reduce the sulfurcontent to a very low level, i.e. 0.030% m/m, which complies with thesulfur limit announced by the International Maritime Organization, to beimplemented in ship fuel by 2020, i.e. 0.5% m/m.

Another advantage carried out by IL1 consists in the fact that it can beused in very low quantity with respect to the oil (the oil/IL1 massratio in the emulsion of example 2 is 450:1) and is capable of beingreused multiple times, until a maximum of 5 times; moreover, the processof extractive desulfurization by IL1 does not require high energy. Thusoverall, the costs related to desulfurization of oils having high sulfurcontent, such as marine fuel oil, are greatly reduced.

Summarizing, the IL composition according to the present invention, andthe process and the apparatus thereof, represent an improvement in thefield of desulfurization of refined crude oil fractions, in particularfor desulfurization of heavy fuel oil and marine fuel oil as they reducethe amount of pollutants in air, employ the minimum energy during thedesulfurisation process, and have a minimal effect on the price of thefuel.

1. An ionic liquid composition to remove sulfur from refined crude oilfraction, comprising two or more compounds having: an imidazolium cationsubstituted by one or more straight or branched C₁-C₆ alkyl group, andan anion selected from the group consisting of R₅COO⁻, Cl⁻, Br⁻, [BF₄]⁻,[PF₆]⁻, [SbF₆]⁻, [R₆SO₄]⁻, [OTs]⁻, [OMs]⁻, wherein R5 is C₁-C₆ alkyl,C₃-C₈ cycloalkyl, benzyl, C₂-C₆ alkenyl, and R6 is C₁-C₆ alkyl.
 2. Thecomposition of claim 1, wherein the imidazolium cation is substituted inposition 1 and 3 by a straight or branched C₁-C₆ alkyl group, optionallyis substituted in position 1 by butyl and in position 3 by methyl. 3.The composition of claim 1, wherein the anion is selected from [BF₄]⁻and [PF₆]⁻.
 4. The composition of claim 1, wherein the two or morecompounds comprise: 1-butyl-3-methyl imidazolium hexafluoro phosphate,and 1-butyl-3-methyl imidazolium tetrafluoroborate.
 5. The compositionof claim 1, wherein the anion is selected from Cl⁻, [BF₄]⁻ and [PF₆]⁻.6. The composition of claim 1, comprising: 1-butyl-3-methyl imidazoliumhexafluoro phosphate, 1-butyl-3-methyl imidazolium tetrafluoroborate,and 1-butyl-3-methyl imidazolium chloride.
 7. The composition of claim6, comprising: from 30 to 50% by volume of 1-butyl-3-methyl imidazoliumhexafluoro phosphate, from 20 to 30% by volume of 1-butyl-3-methylimidazolium tetrafluoroborate, from 25 to 35% by volume of1-butyl-3-methyl imidazolium chloride, with respect to the total volumeof the composition.
 8. The composition of claim 7, comprising: from 35to 44% by volume of 1-butyl-3-methyl imidazolium hexafluoro phosphate,from 22 to 27% by volume of 1-butyl-3-methyl imidazoliumtetrafluoroborate, from 26 to 29% by volume of 1-butyl-3-methylimidazolium chloride, with respect to the total volume of thecomposition.
 9. The composition of claim 6, wherein the volume ratiobetween 1-butyl-3-methyl imidazolium hexafluoro phosphate,1-butyl-3-methyl imidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium chloride is comprised between 1:0.63:0.74 and 1:0.61:0.66.10. The composition of claim 1, wherein the composition (i) does notcomprise an oxidizing agent; and/or (ii) does not comprise a metal salt.11. The composition of claim 1, additionally comprising water and/or anorganic solvent.
 12. A process for desulfurization of a refined crudeoil fraction, comprising: mixing a ionic liquid composition according toclaim 1 with a batch of refined crude oil fraction in a mixing tank tomanufacture an emulsion comprising at least the refined crude oilfraction and the ionic liquid composition; feeding the emulsion througha catalytic reactor to bind at least S-compounds, and optionally othermetals, of the refined crude oil fraction to the ionic liquidcomposition; feeding the emulsion into a settling tank and storing theemulsion in said settling tank for a settling time (t) in order to leavethe S-compounds bond to the ionic liquid composition to separate bygravity from a desulfurized refined crude oil fraction and to settledown in the settling tank; wherein, optionally, the desulfurized refinedcrude oil fraction is then transferred to a storage or service tank;wherein, optionally, the settled ionic liquid composition containingS-compounds is then transferred to a flashing unit.
 13. The process ofclaim 12, wherein, before mixing the ionic liquid composition with thebatch of refined crude oil fraction, the ionic liquid composition ismixed with demineralized water and then the mixture of ionic liquidcomposition and demineralized water is fed to the mixing tank (6)containing or configured to contain the batch of refined crude oilfraction.
 14. The process of claim 12, wherein, in the flashing unit,S-compounds are separated from the ionic liquid composition and form aresidual sludge in the flashing unit; wherein the ionic liquidcomposition free of S-compounds is fed to a separate re-use tank to bereused in the process; wherein the residual sludge is transferred to aholding tank and, optionally, dried and packed for further handling. 15.An apparatus for desulfurization of a refined crude oil fractionconfigured to perform the process of claim 12, wherein the apparatuscomprises: a mixing tank having a first inlet in fluid communicationwith a tank of refined crude oil fraction; a fresh ionic liquidcomposition tank and/or a re-use ionic liquid composition tank in fluidcommunication with a second inlet of the mixing tank; at least onesettling tank having an inlet in fluid communication with an outlet ofthe mixing tank; wherein said at least one settling tank has a firstupper outlet for delivering desulfurized refined crude oil fraction anda second lower outlet for delivering settled ionic liquid compositioncontaining S-compounds; a catalytic reactor located between the outletof the mixing tank and the inlet of said at least one settling tank.